Hydrofoil craft



July 22, 1969 L. w.JoHNsoN 3,456,611

HYDROFOIL CRAFT Filed July 12. 1968 5 Sheets-Sheet 1 Tlcl.-

02d@ 15 WAM@ ATT RNEY5 July 22, 1969 n.. w. JoHNsoN HYDROFOIL CRAFT 5Shets-Sheet 3 Filed July 12, 196e @f1/aga WM5 ATT RNEYS L. W. JOHNSONHYDROFOIL CRAFT July 22, 1969 Filefl July l2. 1968 5 Sheeis-Sheet 4 L.W. JOHNSON HYDROFOIL CRAFT 5 Sheets-Sheet 5 July 22, 1969 Filed July l2,1968 /57/5 Y lNVENTOR United States Patent O 3,456,611 HYDRFGIL CRAFTLew W. Johnson, Rnmson, NJ. (1927 Brightwater Blvd. NE., St. Petersburg,Fla. 33704) Continuation-impart of application Ser. No. 625,513, Mar.23, 1967, which is a continuation-in-part of application Ser. No.521,039, `Ian. 17, 1966. This application `Iuly 12, 1968, Ser. No.747,026

Int. Cl. B631) 1/18 U.S. Cl. 114-665 17 Claims ABSTRACT GF 'THEDISCLOSURE A plural hull watercraft is provided with hydrofoils whichare reversibly adjustable between inoperative positions and operativepositions; the hydrofoils when in an operative position providing ahydroplaning function.

This application is a continuation-impart of my copending applicationSer. No. 625,513, led Mar. 23, 1967, now abandoned, which is in turn acontinuation-impart of my now abandoned application Ser. No. 521,039,filed Ian. 17, 1966.

This invention relates to plural hull watercraft, particularlycatamarans, provided with hydrofoils.

The introduction of hydrofoils for use in watercraft, particularlyseagoing craft, has enabled increased speeds. The typical hydrofoilcraft utilizes at least one hydrofoil which is submerged in the water.The hydrofoil raises the hull of the craft to a higher position inrespect to the water through which the craft is travelling. Thehydrofoil provides an upward component of force or lift when the crafthas forward velocity with respect to the water. When the forwardvelocity of the craft is sufficiently high, the lift created on thehydrofoil by the water raises the entire hull above the surface of thewater and the craft may then be referred to as hydroplaning or being inflight.

There are a number of disadvantages associated with the typicalhydrofoil craft. One problem is rolling and pitching of the craft.Another problem is a sometimes rough transition from a non-hydroplaningstate to a hydroplaning state. Still another problem, not unique tohydrofoil craft, is the expense of drydocking for storage and repairs.Yet another problem is the formation of encrustations on the hydrofoilsand related structure due to continual immersion in the water. Thepresent invention isdirected to providing hydrofoil craft particularlyadapted to overcoming various of these problems and other problems whichwill become apparent from the following description.

In its broadest aspect, the present invention provides a plural hullhydrofoil craft in which at least some hydrofoils are adjustable frominoperative positions for nonhydroplaning to operative positions forhydroplaning. The plural hulls may be referred to individually as hullsections in order to distinguish them from the hull collectively, i.e.,the craft as a whole exclusive of the superstructure.

More specifically, according to one aspect of the present invention,particularly effective operation is obtained by employing to propel thecraft a propulsion system comprising a water inlet duct having an inletport for communication with the body of water on which the craft is tobe propelled, water ejection means in communication with the inlet portto receive water therefrom, an engine drivingly coupled to the waterejection means and a water outlet duct having an outlet port incommunication with the water ejection means to discharge water therefromand with which is provided means to move the inlet port in accordancewith movement of the hydrofoil. Typically, such a water propulsionsystem may be an engine driven turbojet, the water ejection means beinga turbine.

According to another aspect of the invention, a ski-like member isprovided b-etween the hydrofoil and the hull t0 render the transition,from non-hydroplaning to hydroplaning, and vice versa, particularlysmooth.

In further aspects of the invention, the tunnel defined by spacedparallel hull sections is utilized for retraction of hydrofoils andassociated structure above the waterline while the craft is cruising,i.e., not hydroplaning.

According to yet another aspect of the invention, to provide greaterlateral stability of the craft, the craft iS equipped with adjustabledihedral hydrofoils.

The aforementioned features may be employed individually or in variouscombinations.

The retractability of the hydrofoils permits the craft to cruise in anon-hydroplaning state in shallow waters. In those embodiments in whichhydrofoils are retracted above the waterline, there is the furtheradvantage that the hydrofoils are not continually immersed in the waterwhereby the formation of encrustations on the hydrofoils proceeds lessrapidly. Moreover, the adjustability of the position of the hydrofoilsrelative to the hull makes possible compensation of the positions of thehydrofoils for turbulence and waves. Also, as the hydrofoils are raisedand lowered, they remain in an orientation effective for hydroplaningwhereby transitions are smooth. These hydrofoils, furthermore, provide aself-drydocking feature in that the craft may be raised when beached byusing the hydrofoils as jacks.

The feature of the ski member between the hydrofoil and the hull makesfor a smoother transition from the non-hydroplaning state to thehydroplaning state and vice versa. The ski members also serve to deectany debris which may be floating in the water.

The adjustable dihedral hydrofoils provide greater lateral stability.

The invention is further described with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic, side elevational view of one embodiment of ahydrofoil craft laccording to the present invention showing the slopingski-like surfaces and hydrofoil surfaces extending from the bottom ofthe hull;

FIG. 2 is an enlarged, fragmentary side elevational View of the aft endor stern of the craft shown in FIG. 1;

FIG. 3 is a schematic side elevation of another embodiment of ahydrofoil craft according to the present invention showing the slopingski-like surfaces and hydrofoil surfaces extending from the bottom ofthe hull;

FIG. 4 is a front View of the craft shown in FIG. 3, with the fore orbow hydrofoils broken away to show the inlet ducts in the ski-likesurfaces;

FIG. 5 is an elevation View, partly in section, taken along lines 5-5 ofFIG. 4, showing features of the present invention in greater detail;

FIG. 6 is a detailed view of the hydrofoil surface and ski-like surfaceshowing the inlet ports;

FIG. 7 is a detailed elevation View, in section, taken along line 7--7of FIG. 6, showing the hydrofoil and skilike surface retracted withinthe hull;

FIG. 8 is a schematic side elevation view of a hydrofoil craft showing,in the dotted portions, the turbojet engine and propulsion system inwhich the outlet is in a different configuration than that shown in theembodiment of FIG. 3;

FIGS. 9 and 9a are fragmentary front elevations of another embodiment inwhich is illustrated a bow hydrofoil assembly with the hull of the craftappearing in cross section; FIG. 9 illustrates the lassembly in extendedposition and FIG. 9a in retracted position;

FIG. 10 is a fragmentary side elevation from the left side of FIG. 9 butwith more of the hull illustrated;

FIG. 11 is a fragmentary side elevation with the hull partly in crosssection taken on section line 11-11 in FIG. 9, with a dot-and-dashrepresentation being employed to illustrate this portion of the bowassembly also in the retracted position;

FIG. l2 is a fragmentary side elevation, partly in section, taken onsection line 12-12 in FIG. 13, illustrating in extended position a sternhydrofoil and duct assembly employed with the bow hydrofoil assembly ofFIGS. 9 t 11, with a dot-and-dash representation being employed toillustrate the stern assembly also in the retracted position;

FIG. 13 is a fragmentary front elevation, partly in section, taken onsection line 13-13 of FIG. 12; and

FIG. 13a is analogous to FIG. 13 but illustrating the stern assembly inretracted rather than extended position.

Referring now to FIGS. 3 and 4, a hydrofoil craft is shown comprising ahull 12 which is adapted to float in the water, when the craft is atrest, or travelling at relatively low speeds.

Forward and aft hydrofoils 14 and 16 are provided for dynamic support ofthe craft after it gets under way and hull 12 is raised entirely out ofthe water. The hydrofoils 14 and 16 are disposed sufficiently away fromthe hull to avoid substantial wave impact against any portion of thehull when the craft is riding on the hydrofoils. Fore and aft slopingski-like surfaces 18 and 20, are disposed between the hydrofoils 114 and16, respectively, land the hull 12, and slope upwardly from the end ofthe hydrofoils to a position within the hull 12. The ski-like surfaces18, 20 also serve to protect the hydrofoil surfaces 14, 16 by deflectingfloating objects which would otherwise strike the hydrofoil surfaces.

The hydrofoil surfaces 14 and 16 are positioned relative to the hull bythe vertical movement of rods which are connected to the top surface ofthe hydrofoil by connecting means 23. As more fully described below, theposition of rod 25 is controlled by a hydraulic control system.

As shown in FIG. 4, the craft, by way of example, is essentially in theform of a catamaran having port and starboard sections, each of whichhas essentially similar ski-like surfaces and hydrofoil surfacesextending from the bottom surface thereof.

A turbojet water propulsion system is provided to supply forwardvelocity to the craft. The system takes up `water from the sea throughan inlet port 22 which extends through sloping ski-like surface 20 fromwhere it is sucked through a flexible duct 27, into a turbine 26.Turbine 26 is driven by an engine 24 or turbine. The turbojet 26exhausts the liquid through a duct 29 and out from an exhaust port 21. Ascreen 28 is positioned over the inlet port 22 to prevent any debrisfrom clogging the port and to insure trouble-free operation.

FIG. 3 shows one feature of the invention, in which the outlet port 21is positioned with respect to the aft hydrofoil surface 16, to increasethe eiliciency of the water jet propulsion system. The exhaust or outletport 21 is positioned to exhaust at that location in the stern of eachhull or from each rear hydrofoil surface 16 to insure the optimumefficiency of operation of the turbojet.

FIG. 5 provides `a more detailed structural view of the hydrauliccontrol system for the hydrofoil and skilike surfaces. The rod 25 isfixedly connected to the lower end of a piston 30 which moves within acylinder 32.

The movement of piston 30 is controlled by the introduction of hydraulicfluid into cylinder 32. The hydraulic fluid input to the cylinder isresponsive to operations from a control system 43. Height sensors 42 aremounted to the craft at any convenient location on either side of thecraft, land to the fore and aft sections of the craft. A velocity sensory45 is also mounted to sense the forward velocity of the craft. Bothsensors are coupled to a control apparatus 43, which processes the datareceived to send a mechanical signal to the hydrofoil contro-l cylinders32 to raise or lower the pistons 30. The sensors and control apparatusmay be similar to that shown in U.S. Patent No. 3,149,601.

Due to disturbances in the water surface such as waves, the relativeheight of the several hydrofoil surfaces may be unbalanced. The heightsensors 42 sense the heights of each of the hydrofoil surfaces. Thisdata is processed by the control computer 43 which may be hydraulic,mechanical, or electronic in nature. The resulting signals are comparedto a reference signal, which is a function of the craft velocity asdetermined by velocity sensor 45. The control computer 43 then transmitsmechanical signals through the mechanical linkage means 44 to equalizethe pressure within the hydraulic cylinders 32 thereby stabilizing thecraft by equalizing the relative positions of the several hydrofoilsurfaces.

For this purpose pressure sensing means (not shown) may be used insteadof the height sensing means to transmit data to the control computer.The hydraulic system is operated automatically in response to theforward velocity of the boat Within the water as sensed by velocitysensor 45. As the velocity increases, control computer 43 transmits .amechanical signal to cylinders 32 through linkage means 44 to cause therod 25 to descend in a substantially vertical direction, to lower thehydrofoils and ski-like surfaces into the water.

However, it should be noted that the hydraulic system not only operatesthe hydrofoils, but is also capable of lifting the hydrofoil craft whentbeached. Thus the hydraulic system acts as a jack and facilitates alldrydocking operations, like hull painting, or any other repairs. By thisdual functioning of the hydraulic system, namely to operate thehydrofoils and serving as a jack to lift the craft for drydockingoperations, the necessity of cradling or blocking of the craft iscompletely eliminated.

As shown in FIG. 5, in which the hydrofoil 14 and skilike surface 18 arealready positioned below the hull, the ski-like surfaces 18 and 20extend at a sloping angle to a pivot position 31 located within thehull. The ski-like surfaces 18 and 20 are pivotally connected at theother end thereof to the hydrofoil surface 16 and 14 by means of a pin35.

As best seen in FIG. 6, each ski-like surface is a substantially flatsurface which is narrow at the end which is fixed to the hydrofoilsurface. The ski-like surface widens towards the end at which it joinswith the hull.

In operation, as the velocity of the craft increases, the hull risesfrom the water. The craft then proceeds to travel along the ski-like andhull surfaces until the speed is further increased, so that the hullthen rises further and the boat rides along the hydrofoil surfaces.During this increase in craft velocity, the hydrofoil surfaces aregradually lowered into position by the hydraulic control system.

A further feature of the present invention is the provision of an airdome, or air cushion 37, within each hydraulic cylinder 32 to provideshock absorption for the craft from any water turbulence, or impactcaused by a hydrofoil Istriking a floating object. A sudden jarring ofthe hydrofoil 4will be transferred to piston 30 within the cylinder 32.The air cushion 37, positioned at the upper portion of the cylinder 32,will receive the sudden motion of the piston, and `will thereby cushionthe shock by allowing the particular hydrofoil to deflect and quicklyreturn to its former position through the resilient `action of the aircushion. This may be employed in each cylinder of each embodimentdisclosed herein.

This feature will greatly smooth the operation of the hydrofoil crafteven in the most turbulent of waters.

As shown in FIG. 7, when the craft comes to rest, or rides on the hullsurface at low velocities, the hydrofoil surface 14 and ski-like surface18 are retracted into a recess 41, located yat the bottom of the hull.This retraction Iis effected by moving piston 30 along with linking rod25 upwards. The hydrofoil and ski-like surface pivot into the retractedposition about pivot pins 31 and 35. The same action may also beprovided for members 16 and 20f-at the aft end of the craft.

The embodiment yin FIG. 8 is quite similar to that shown in FIG. 3,except that the outlet port 40 exhausts the jet stream at a level withinthe hull.

The embodiment shown in FIGS. 1 and 2 illustrates the -alternativeconstruction of a turbojet water propulsion system which can be used inthe water going craft of the present invention. In this embodiment theski-like sloping surfaces such as indicated by the reference characters18 and 20 in FIGS. 3, 5, 6 and 8 are eliminated at the fore and aft endsof the craft. Hydrofoil 16 is supported, in part, by strut means 50pivotally connected to the bottom of the hull at 52 and to the hydrofoilsurface at 23'. The hydrofoil surface 16' is also supported by rod 25'that is coupled to piston 30 of cylinder 32'. Hydrofoil surface 14' issupported, in part, by strut means 51 pivotally connected to the bottomof the hull at 53 and to the hydrofoil surface at 23. The movement ofthe hydrofoil 14 and 16 are controlled #by an hydraulic system identicalto that described in connection with the previous embodiment and whichis synchronized with the speed of the craft. Accordingly the descriptionof the control system need not be repeated at this time.

Means to take up water from the sea for propulsion purposes is providedby an inlet port 22 which extends from hull 12 from where it is suckedthrough a duct 27 into a turbine 26. Turbine 26 is driven by an engine24'. The turbojet exhausts the liquid through a duct 29 and out fromexhaust port 21. The portion of the free end of inlet port 22 that lisin communication with the water is adjustable by means ofA a rod 54coupled to piston 56 of cylinder 58. The aforementioned hydrauliccontrol system couples the movement of the inlet port to that ofhydrofoil surface 16.

In FIGS. 9 to 13a is illustrated an embodiment in which the turbojetinlet ducts and most of the hydrofoil surfaces `are retractable into thetunnel between the hulls with the thus retracted hydrofoil surfaces andla portion of the thus retracted inlet ducts above the Waterline wherebyharmful encrustation of the hydrofoil surfaces by prolonged immersion inthe water is avoided and a bow hydrofoil assembly is provided withrotatable dihedral foils adjustably to provide greater lateral stabilityof the craft while in flight.

In this embodiment the bow hydrofoil assembly 100 (FIGS. 9, 9a, 10 andl1) lis comprised of a center hydrofoil 101 which is horizontallaterally and identical di- =hedral hydrofoils 102 and 103 which arevery closely adjacent to or abut against the center hydrofoil 101.Hydrofoils 102 and 103 are rotatable between a position in which they`are laterally horizontal and therefore in lateral alignment with thehydrofoil 101 to la position rotated 30 upward from the horizontal andintermediate positions, hydrofoils 102 and 103 defining a dihedron whenin a so rotated position.

Hydrofoil 101 is supported by identical rods 1014 and 106 and identicalstruts 107 and 108. The rod 104 and the strut 107 are pivotallyconnected to the hydrofoil 101 by means of a bracket 109 rigidly mountedon the hydrofoil 101 and the rod 106 and the strut 108 are similarlyconnected to the hydrofoil 101 by means of a -bracket 110. The other endof struts 107 and 108, respectively, are pivotally connected to the topof the tunnel between the hulls by means of brackets 111 and 112. Theother end of rods 104 and 106, resepectively, are rigidly connected topistons 113 and 114. The pistons 113 and 114, respectively, are slidablymounted in hydraulic cylinders 115 and 116.

Retraction of the hydrofoil 101 is effected by activation of thehydraulic cylinders 115 and 116 to retract the pistons 113 and 114 andtherewith the rods 104 and 106.

The rods and 121 are pivotally connected to the hydrofoil 102 by meansof brackets 122 and 123, respectively, each provided ywith a slot forsliding therein of the pivot pin. Similarly, the hydrofoil 103 issupported by rods 124 and 125 pivotally connected to the hydrofoil 1013by means of like brackets 126 and 127, respectively. The identical rods120, 121, 124 and 125 are rigidly connected to identical pistons 128,129, 130 and 131, respectively, the pistons 128, 129, 130 and 131 beingslidably mounted in identical hydraulic cylinders 132, 133, 134 and 135,respectively.Cylinders 133 and 135 are controlled together as arecylinders 132 and 134 in order that the dihedral angle may be varied.Cylinders 132 and 134 may be activated independently of or incoordination with the cylinders 133 and 135 in order to permit,alternatively, adjustment of the average elevation of the hydrofoils 102and 103 without adjustment of the dihedral angle, adjustment of thedihedral angle without adjustment of the elevation of the inner edges ofthe hydrofoils 102 and 103 and simultaneous adjustment of the avergeelevation and the dihedral angle of the hydrofoils 102 and 103.

The hull bottoms and 141 are laterally inclined from the horizontal by30. In the retracted position, the upper surfaces of the hydrofoils 102and 103 abut the respective hull bottoms 140 and 141, the dihedral angleadjusted to 30. This is the preferred arrangement though, the hullbottoms may be provided with no inclination or one which is less than30, in which event the dihedral angle of the hydrofoils 102 and 103would be adjusted during retraction to the corresponding value. Thehydro foil 101 is operated independently of the hydrofoils 102 and 103because the vertical distance the hydrofoil 101 must travel to becomeoperative is greater than the vertical distance to be traversed by thehydrofoils 102 and 103. Preferably, vertical movement of the hydrofoil101 on the one hand and the hydrofoils 102 and 103 on the other hand iscoordinated so that the hydrofoil 101 is lowered to the level of theinner edges of the hydrofoils 102 and 103 before lowering of thehydrofoils 102 and 103 begins, optionally the provision being made forlocking of the hydrofoils into a unitary assembly at this level, andsubsequently through further lowering the hydrofoils 101, 102 and 103move in unison. Retraction proceeds exactly in the reverse.

The stern assembly (FIGS. 12, 13 and 13a) is comprised of a hydrofoil151 and for the turbojet propulsion system identical rigid water inletducts 152 and 153 provided with screens 152a and 153a at their inletports. The stern assembly is supported by identical rods 154 and 155pivotally mounted to the hydrofoil 151 by means of respective brackets156 and 157, which brackets also pivotally mount ducts 152 and 153respectively. Toward their other end the ducts 152 and 153 are pivotallymounted on the inner walls of the respective hulls near the top of thetunnel by means of respective joints 158 and 159. The rods 154 and 155are rigidly connected to respective identical pistons 160 and 161, thepistons 160 and 161 in turn being slidably mounted in respectiveidentical hydraulic cylinders 162 and 163. Identical brackets 164 andiixed to the roof of the tunnel pivotally mount the cylinders 162 and163, respectively. The cylinders 162 and 163 are controlled together.

Retraction of the stern assembly into the tunnel with the entireassembly but for a lower portion of the ducts 152 and 153 above thewaterline is effected simply by activation of the cylinders 162 and 163to retract the pistons 160 and 161. The suspended end of the assemblythus swings forwardly and upwardly into the tunnel to a rest positionabutting the ceiling of the tunnel. Extension of the assembly to theoperative position is by exactly the same operation in reverse.

-By means of height sensors 42, a velocity sensor 45 and linkage means43, as in the other embodiments (see FIGS. l, 3 and 8), the craft 4maybe stabilized by equalizing the relative positions of the hydrofoils 101and 151. Moreover, a rolling sensor may be linked to the cylinderscontrolling the dihedral angle of the hydrofoils 102 and 103automatically to provide optimum lateral stablility by increasing of thedihedral angle in response to an increase in rolling thereby to decreasethe rolling.

While I have described certain embodiments of my invention, I desirethat the scope of my invention be limited only by the scope of theappended claims.

What is claimed is:

1. A craft comprising a hull constituted of a plurality of hullsections, hydrofoil surface means operatively connected to said hull foradjustment of the height of the hydrofoil surface means relative to saidhull, means to lower said hydrofoil surface means from an inoperativeposition to an operative position while maintaining said hydrofoilsurface means in an orientation to continuously provide a hydroplaningfunction, to support said hull when said craft reaches a predeterminedspeed, a propulsion system secured to said craft and arranged to propelsaid craft through a body of water, said propulsion system comprising awater inlet duct having an inlet port for communication with the body ofwater, water ejection means in communication with said inlet port toreceive water therefrom, an engine drivingly coupled to said waterejection means and a water outlet duct having an outlet port incommunication with said water ejection means to discharge watertherefrom, and means to move said inlet port in accordance with themovement of said hydrofoil surface means.

2. A craft in accordance with claim 1, wherein said water ejection meansis a turbine.

3. A craft in accordance with claim 1 including a ski-like memberextending between said hydrofoil surface means and said hull sectionassociated therewith.

4. A craft in accordance with claim 1 including a skilike memberextending between said hydrofoil surface means and said hull sectionassociated therewith and movable together with said hydrofoil surfacemeans, said inlet port being disposed in at least one of said ski-likemembers.

5. A craft in accordance with claim 1 wherein said water inlet ductextends downwardly from at least one of said hull sections whereby saidinlet port is in communication with the water.

6. A craft in accordance with claim 1 wherein said outlet portterminates above said hydrofoil surface means.

7. A craft in accordance with claim 1, in which said means to lowersai-d hydrofoil surface means comprises an hydraulic system including acylinder, a piston movable within said cylinder and means connectingsaid piston to said hydrofoil surface means.

8. A craft in accordance with claim 7 including air cushion meanscoupled to said cylinder and arranged to absorb at least part of themovement of said piston.

9. A craft in accordance with claim 1 including means to sense theheight of said hydrofoil surface means, means to provide a signalcorresponding in magnitude to the height sensed and hydrofoil actuationmeans responsive to said signal means.

10. A craft in accordance with claim 9 including an hydraulic systemarranged to move said hydrofoil surface means, said actuation meansbeing coupled to said hydraulic system for actuation thereof.

11. A craft comprising a hull, hydrofoil surface means operativelyconnected to said hull to support said hull when said craft reaches apredetermined speed, a ski-like member extending between said hydrofoilsurface means and said hull and propulsion means secured to said craftand arranged to propel said craft through water.

12. A craft according to claim 11, in which said hydrofoil surface meansis movable.

13. A craft according to claim 12, in which said skilike member ismovable with said hydrofoil surface means,

14. A craft adapted to travel on a body of water and comprising a hullconstituted of a plurality of hull sections defining atleast one tunneltherebetween, said tunnel being open at the bottom and extendingupwardly beyond the waterline of the craft, hydrofoil surface meansoperatively connected to said hull for adjustment of the position ofsaid hydrofoil surface means relative to the hull and means reversiblyto adjust the position of said hydrofoil means relative to the hull froma fully retracted position in which the hydrofoil means is retractedinto said tunnel above said waterline to extended positions in which thehydrofoil means is positioned below the waterline to provide a.hydroplaning function.

15. A craft according to claim 14, further comprising propulsion systemsecured to said craft and arranged to propel the craft through water,said propulsion system comprising at least one water inlet duct havingan inlet port arranged for communication with the body of water and saidduct being arranged to move to change the position of the inlet portrelative to the hull in accordance with the movement of the hydrofoilsurface means.

16. A craft according to claim 15, in which `the duct is so arrangedthat it is positioned partly above the waterline when the hydrofoilsurface means is in its fully retracted position.

17. A craft according to claim 15, in which said hydrofoil surface meansand said `duct are positioned toward the stern of the craft.

References Cited UNITED STATES PATENTS 3,236,202 2/1966 Quady et al114-665 FOREIGN PATENTS 553,450 5/1943 Great Britain.

ANDREW H. FARRELL, Primary Examiner

